Light-emitting diode (LED) light sources (e.g., LED light engines) are often used in place of or as replacements for conventional incandescent, fluorescent, or halogen lamps, and the like. LED light sources may comprise a plurality of light-emitting diodes mounted on a single structure and/or provided in a suitable housing, for example. LED light sources are typically more efficient and provide longer operational lives as compared to incandescent, fluorescent, and halogen lamps. In order to illuminate properly, an LED driver control device (i.e., an LED driver) may be coupled between an alternating-current (AC) source and the LED light source for regulating the power supplied to the LED light source. The LED driver may regulate either the voltage provided to the LED light source to a particular value or the current supplied to the LED light source to a specific peak current value, or may regulate both the current and voltage.
LED light sources may be rated to be driven via a number of different control techniques including, for example, a current load control technique or a voltage load control technique. An LED light source that is rated for the current load control technique may be characterized by a rated current (e.g., approximately 350 milliamps) to which the peak magnitude of the current through the LED light source should be regulated to ensure that the LED light source is illuminated to the appropriate intensity and color. In contrast, an LED light source that is rated for the voltage load control technique may be characterized by a rated voltage (e.g., approximately 15 volts) to which the voltage across the LED light source should be regulated to ensure proper operation of the LED light source. One or more parallel strings of LEDs in an LED light source rated for the voltage load control technique may include a current balance regulation element to ensure that the parallel strings have similar impedance so that similar current may be drawn in each of the parallel strings.
LED drivers may be configured to dim the light output of an LED light source. Example methods of dimming LEDs include a pulse-width modulation (PWM) technique and a constant current reduction (CCR) technique. Pulse-width modulation dimming may be used for LED light sources that are controlled in a current or voltage load control mode, for example. In pulse-width modulation dimming, a pulsed signal with a varying duty cycle is supplied to the LED light source. If an LED light source is being controlled using the current load control technique, the peak current supplied to the LED light source is kept constant during an on time of the duty cycle of the pulsed signal. However, as the duty cycle of the pulsed signal varies, the average current supplied to the LED light source may also vary, thereby varying the intensity of the light output of the LED light source. If the LED light source is being controlled using the voltage load control technique, the voltage supplied to the LED light source is kept constant during the on time of the duty cycle of the pulsed signal in order to achieve the desired target voltage level, and the duty cycle of the load voltage is varied in order to adjust the intensity of the light output. Constant current reduction dimming may be used, for example, when an LED light source is being controlled using the current load control technique. In constant current reduction dimming, current may be continuously provided to the LED light source while the DC magnitude of the current provided to the LED light source may be varied to thus adjust the intensity of the light output. Examples of LED drivers are described in greater detail in commonly-assigned U.S. Pat. No. 8,492,988, issued Jul. 23, 2010, entitled CONFIGURABLE LOAD CONTROL DEVICE FOR LIGHT-EMITTING DIODE LIGHT SOURCE, and U.S. Patent Application Publication No. 2013/0063047, published Mar. 14, 2013, entitled LOAD CONTROL DEVICE FOR A LIGHT-EMITTING DIODE LIGHT SOURCE, the entire disclosures of which are hereby incorporated by reference.
If the LED light source is being controlled using the voltage load control technique, the magnitude of the voltage at the output of the LED driver may differ from the magnitude of the voltage across the LED light source due to, for example, the impedance of the electrical wiring between the LED driver and the LED light source. Accordingly, the magnitude of the voltage across the LED light source may not be equal to the rated voltage of the LED light source. In addition, under the example scenario described herein, the length of the electrical wiring between the LED driver and the LED light source may vary from one installation and/or circuit to the next. As a result, the magnitude of the voltage across the LED light source and thus the intensity of the LED light source may vary from one installation and/or circuit to the next for a given output voltage of the LED driver. If there are multiple installations of LED light sources controlled by a single LED driver in a room and each of LED light sources has a different length of electrical wiring between the LED driver and the respective LED light source, the intensities of all of the LED light sources may appear different to an occupant of the room, which is undesirable.